The Spider Demon blinked several times, its many eyes narrowing in bewilderment. The boy—this terrified, trembling wreck of a human—was clinging to a branch high above, crying and shouting incoherently. His body shook like a leaf in a storm, his voice rising and falling between sobs and screams.
"What kind of Demon Slayer are you supposed to be?" The creature rasped, its tone halfway between amusement and contempt. Its grotesque, human-like face twisted into a smirk. "Crying and screaming won't stop the poison. Just give up already."
Zenitsu, barely hearing it, sniffled and wailed louder, hugging the tree branch as if it could save him. "I don't want to die! I'm too young to be ugly! I haven't even gone on a date yet!"
The demon's clawed legs twitched in annoyance. Around its massive form, the human-headed spiders began to scuttle upward, their distorted faces grinning eagerly. "Then stop whining and let it happen quickly," the spider hissed, gesturing for its spawn to climb.
Zenitsu looked down and paled. "WAIT! WAIT! Hold on a sec—just—just give me a moment!" he yelled, holding out his hands as if trying to negotiate with his death. "Let me—let me think!"
He gripped his head in frustration, tugging at his hair as panic overwhelmed him. Clumps of yellow strands came off in his hands, fluttering away in the breeze. "WHAT?! My hair?! My beautiful hair!" he cried. "No one told me I'd go bald first! This poison is the WORST!"
The Spider Demon burst into laughter, the sound a wet, guttural rattle that echoed through the forest. "Baldness is the least of your problems, boy! You'll lose much more than that when your bones start bending!"
Zenitsu's breathing became ragged, his vision swaying. The venom's burning sensation pulsed through his body like fire. His trembling grew worse until, finally, his eyes rolled back—and he went limp.
He collapsed, falling from the branch.
The Spider Demon blinked again, confused. "Did… he just faint?" it muttered.
Zenitsu's unconscious body fell toward the ground, limbs loose, his sword dangling from its sheath. The demon tilted its head, trying to make sense of the bizarre sight. "That's it? He fainted? This is the one the Demon Slayer Corps sent to kill my family?" it scoffed, disgusted.
But before his body could hit the ground, something changed.
Zenitsu's breathing slowed—steady, rhythmic. His body tensed midair, twisting smoothly. His hand found the hilt of his sword without thought. His eyes remained closed, but his expression shifted—from fear to calm.
He planted both feet against the side of a tree trunk just before impact, lightning faintly sparking around him. With a sharp exhale, he launched himself back into the air.
BOOM.
The explosion of wind and sound startled even the Spider Demon, which reeled backward as Zenitsu soared toward it, sword drawn, his hair glinting gold under the moonlight.
The demon recovered quickly and hissed, puffing out its chest. "Poison Sputum!"
A glob of dark green acid shot from its mouth, sizzling through the air. Zenitsu twisted at the last moment, barely avoiding it as it splattered against a nearby tree, melting through bark and wood like boiling oil.
When he landed, he did so lightly, crouching with perfect balance. His blade shimmered faintly with electricity, his expression serene.
The Spider Demon's grin faltered. "What… what happened to him?" it muttered, its voice full of uncertainty. "His movements… his aura… it's completely different."
The smaller spiders around it hesitated, chittering nervously. The boy in front of them wasn't the same coward who'd been screaming moments ago. This one stood straight, his breathing deep and measured, his presence sharp and suffocating.
Zenitsu's hand tightened on his sword hilt. "Thunder Breathing…" he murmured softly, his voice calm and steady even in sleep.
The demon flinched, sensing danger. "Kill him!" it commanded.
The swarm of spiders leapt at Zenitsu from every direction—front, behind, and above. Their human faces screamed, cried, and laughed as they lunged. Zenitsu didn't flinch. He simply slid his foot slightly forward, lowering his stance again.
The Spider Demon laughed, convinced it had figured him out. "So that's all you can do, huh? The same stance again and again? Pathetic! You're just repeating the same motion!"
It spat another blob of poison, hurling it toward him with lethal speed. Zenitsu darted aside in a flash, his movements a blur. The acid struck the ground where he had been, leaving behind a smoking crater.
But when Zenitsu landed again—his stance hadn't changed.
His knees were bent just right, his sword angled precisely toward the ground, lightning still crackling faintly at his feet. His breathing came in long, measured bursts, his face composed, his eyes still closed.
The Spider Demon's grin returned, cruel and gloating. "You only have one trick! One form! And you think that'll save you?!"
It clicked its mandibles and sent its spider brood swarming again, filling the forest floor with chittering bodies. The sound of their claws on bark was deafening, the smell of poison thick in the air.
But Zenitsu didn't move.
He stood perfectly still, his sword trembling slightly with contained energy.
Thunder rumbled faintly above. The forest seemed to hold its breath.
The Spider Demon, sensing the building power, hesitated for the first time. The boy's stillness wasn't weakness—it was focus. The faint sparks around him grew brighter, running up his blade like veins of light.
"What… what are you doing?" the demon hissed, suddenly unsure.
Zenitsu exhaled, whispering softly, almost reverently—
"Thunder Breathing, First Form: Thunderclap and Flash."
Then—lightning exploded.
The air screamed as Zenitsu vanished, his body becoming a streak of blinding yellow that tore through the forest like divine wrath. The ground split beneath the pressure wave, and in a single heartbeat, he reappeared—behind the Spider Demon, blade drawn in a clean, swift arc.
The demon froze, its laughter cut short.
A thin line appeared across its neck.
Zenitsu slowly sheathed his sword, his body trembling as the electricity around him faded.
The Spider Demon's head slid off its shoulders, hitting the ground with a dull thud. Its body twitched, spasming as its eyes dimmed.
It managed a weak chuckle, whispering through the last remnants of its strength, "H-he only had… one form…"
~~~